1. Field of the Invention
The present invention generally relates to modem communications and, more particularly, to systems and methods for increasing speed and improving performance of modems.
2. Related Art
As the popularity of the Internet continues to increase, consumers and Internet Service Providers (ISPs) seek new methods and systems for providing data at a higher throughput in a way that requires minimal expense and retrofitting at the subscriber's premises. The need for transferring data at higher rates has been intensifying day by day due to the increased use of the Internet to transfer image files, video files and the like files, which contain a great amount of data. Such need has caused many users to transition away from traditional voiceband analog modems, with a top data rate of about 56,000 bits-per-second (bps) downstream and about 33,000 bps upstream, to more expensive broadband alternatives such as DSL modems, cable modems, T1 or T3 lines. However, it is well known that such alternatives suffer from many drawbacks when compared to analog modems. For example, (1) such alternatives are not versatile and unlike analog modems may not be simply plugged into any phone line that can support voice and all legacy voiceband modem and fax services, (2) DSL and cable services may not be available in many locations, (3) such alternatives need retrofits at both central site and the client premises, and (4) such alternatives are considerably more expensive and take more time to be set up.
On the other hand, modems are less expensive, more versatile and take less time to be set up and placed in use, because they take advantage of the existing telephony infrastructure provided by copper wire pairs and linecards, which are used to provide telephony services. Copper wire pairs are also referred to as a loop and essentially extend from a customer's premises and terminate at a linecard in a telephone company central office. Line cards and associated line card shelf circuitry at the central office are used to transmit signals on copper wires and to link copper wires to central office switching equipment.
FIG. 1 illustrates a conventional communication system or model 100 using traditional analog modems (e.g., modems configured in accordance with V.34, V.90 or V.92 standards). As shown, communication system 100 includes client side modem 110 for use by an end-user, such as a modem in a personal computer at home or office. Client side modem 110 receives user data 105 in digital form from the personal computer (not shown) and converts user data 102 to analog form (modulated data) for transmission as analog signal 112 over the local loop to the central office. In addition, client side modem 110 receives analog signal 115 over the local loop from the central office and converts analog signal 115 to digital form and transmits user data 105 to the personal computer. As discussed above, the local loop carrying analog signals 112 and 115 terminates at linecard 120 located at the central office. For example, linecard 120 receives analog signal 112 from client side modem 110 and provides A/μ-law digitized analog signal 122 to central site modem 140 over digital switching network 130, and further receives A/μ-law digitized analog signal 125 from central site modem 140 and provides analog signal 115 to client side modem 110.
As shown in FIG. 1, A/μ-law digitized analog signal 122 is transmitted over digital switching network 130 and received as A/μ-law digitized analog signal 132 by central site modem 140, which converts A/μ-law digitized analog signal 132 to user data 142 in digital form (or demodulated data) for use by a remote device, such as Internet Service Provider (“ISP”) 150. Similarly, ISP 150 transmits user data 145 in digital form to central site modem 140 for conversion to A/μ-law digitized analog signal 135 and transmission over digital switching network 130, which signal is received by linecard 120 as A/μ-law digitized analog signal 125 and provided to client side modem 110 over the local loop as analog signal 115 for conversion to user data 105 and use by the computer or terminal at the client premises.
It is the conversion to A/μ-law PCM at 8 kHz sample rate that generally is the main impairment that limits the data rates, which imposes a theoretical maximum connection speed of 64 kbps and a practical limit of below 56 kbps, as provided by traditional modems supporting V.92/V.90 modulation. Furthermore, such modems must determine and compensate for digital network impairments, far end echo, send answer tone to turn off echo suppressor and echo canceler existing in communication system 100. In addition, traditional modems must always dial a phone number prior to establishing a connection, which requires long training period to achieve.
Moreover, a commercially available broadband alternative, such as DSL, also falls short of being a complete solution. For example, DSL is defined primarily to achieve very much higher speeds of up to several mega bits per second, and uses less complex modulation schemes to aid hardware implementation of the highest available speeds. As a result, DSL service is not available on many lines that can support a substantially higher data rate than 56 kbps, but cannot support the lowest provided speeds of current DSL technology.
Accordingly, there in an intense need to provide a new and revolutionary communication model, which provides substantially higher data rates for modems and eliminates current limitations and impairments in today's modem communication systems. There is also a long-felt need for new communication models using existing copper wire infrastructure, with minimal upgrade, which can provide data rates commensurate with existing digital lines and that can eliminate the need for time consuming and expensive installations of new infrastructure for T1, T3 and DSL lines.